Scanning antenna having a cylindrical splash plate for providing linear beam motion



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United States Patent SCANNING ANTENNA HAVING A CYLINDRICAL SPLASH PLATE FOR PROVIDING LINEAR BEAM MOTION Alan R. Mace, Millersville, Md., and Jacob Tellier, Milwaukee, W1s., assignors, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed May 10, 1963, Ser. No. 279,642 4 Claims. (Cl. 343-754) The present invention relates to improvements in scanning antennas and more particularly to scanning antenna structures having a fixed radiator and a rotatable cylindrical splash plate for providing linear beam motion.

Various methods of scanning a radar beam are employed in the radar art. In one method, a source of radiation is placed at the axis of symmetry of a rotating reflector and the reflector is tilted either about the focal point of the reflector by an amount equal to the scan angle or about the vertex of the reflector by an amount equal to half the scan angle. The axis of rotation always coincides with the axis of symmetry. This method of scanning operates satisfactorily at low scan rates, but becomes impractical at very high scan rates because of dynamic unbalances of the reflector.

Another method of scanning a radar beam is to provide a stationary reflector and move the radiator through a circular path in a plane passing through the focal point of the reflector and being perpendicular to the axis of the reflector. While this method has been used successfully at low scan rates, it has been found that at high scan speeds major mechanical problems make this method impractical.

Another method of scanning a radar beam is to rotate a dielectric lens that is placed in the path of radiation between the source of radiation and a reflector. The dielectric lens produces an image of the radiator in a plane passing through the focal point of the reflector and perpendicular to the axis of the reflector. This method of scanning is also impractical because of the extremely low transmission etliciency of the dielectric lens due to the large amount of electromagnetic radiation which is reflected at the inner and outer surfaces of the dielectric lens. Also the use of dielectric lens in conjunction with Waveguides causes attenuation by a serious impedance mismatch which further reduces the efliciency of the system.

The present invention relates to a method of achieving rapid linear antenna beam scanning by providing a stationary reflector and waveguide feed and by rotating a cylindrical splash plate that is mounted in front of the waveguide feed. A spiral trough is provided around the periphery of the cylindrical splash plate and various types of scan, such as sawtooth, linear, or sine wave, are achieved depending upon the particular configuration of the trough. The trough in the cylindrical splash plate may be either physical or electrical, that is, the trough may be physically cut into the cylinder in the desired pattern or the trough may be made to appear electrically by means of dielectric materials located around the cylindrical surface.

It is therefore a general object of the present invention to provide an improved scanning antenna that will achieve rapid linear antenna beam scanning.

Other objects and advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein:

FIGURE 1 is a side view showing a preferred embodiment of the present invention;

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FIGURE 2 is a top view of the embodiment shown in FIGURE 1;

FIGURE 3 is a sectional view taken through the center of splash plate 13;

FIGURE 4 is a top view of a cylindrical splash plate having dielectric material thereon;

FIGURE 5 is a sectional view taken on line 5--5 of FIGURE 4;

FIGURE 5(a) is a diagrammatic view showing an equivalent plate for the dielectric material shown in FIG- URE 5.

FIGURES 6(a), 6(b), and 6(c) are diagrammatic views showing scanning patterns; and

FIGURE 7 is a diagrammatic view showing a layout of a pair of troughs for producing a sawtooth type of scan.

Referring now to the drawing, and particularly to FIGURES 1-3, there is shown a waveguide radiator 11 and a reflector 12 that are both stationarily attached to a frame (not shown). The aperture of waveguide radiator 11 extends beyond the edge of reflector 12. A cylindrical splash plate 13 is rotatably attached to reflector 12 by means of support arms 14 and 15,and is positioned adjacent the aperture of radiator 11. As best shown in FIGURE 3 of the drawing, bearings 16 and 17 are provided on the inside base of splash plate 13 and support arms 14 and 15 are mounted in the inner races thereof. A motor 18 is attached to support arm 15 by means of motor bracket 19, and a spur gear 21 is attached to motor shaft 22. An internal tooth gear 23 is provided on the inner base of splash plate 13, and meshes with spur gear 21.

An off-center trough 24 is provided in the outer surface of splash plate 13 and spirals around the periphery thereof. The slope of trough 24 determines the type of scan that will be made. For example, if trough 24 is cut linearly around the periphery then the scan pattern will be linearly as shown in FIGURE 6(a). A slight modification of trough 24 will provide a sine wave scan, as shown in FIGURE 6(b).

By providing a pair of troughs 25 and 26 as shown by the diagram in FIGURE 7 of the drawing, a sawtooth type of scan, as shown in FIGURE 6(c), can be provided. Trough 25 begins at point A which is at a full left deflection position and then proceeds through point B to point C, which is displaced degrees and is at a full right deflection position. Trough 26 then becomes operable and starts at point D, which is at a full left position and then proceeds through point E to point F, which is at a full right position. Rotation of splash plate 13 one full revolution will provide a scan from full left to full right followed by an immediate shift again to full left and then to full right, as shown in FIGURE 6(c), which results in a sawtooth type of scan.

In operation, a transmitter (not shown) which is coupled to waveguide radiator 11 provides RF energy which is radiated in a straight line from radiator 11. This energy strikes the trough in splash plate 13 and is then reflected to reflector 12 from which it is then reflected into space in search of a target. Splash plate 13 is rotated when motor 18 is energized and thus the reflected beam is caused to scan.

Referring now to FIGURES 4 and 5 of the drawing, there is shown a cylindrical splash plate 31 that is provided with an electrical trough that is produced by the bands of dielectric materials 32 through 39. By Way of example, the bands have tapered dielectric constants with the materials having the highest values being placed such that they would appear to produce the deepest part of the trough. FIGURE 5(a) of the drawing shows an equivalent curve metal plate 41, the configuration of which would produce a scan pattern similar to that produced by splash plate 31. A trough may also be made to appear electrically by varying the thickness of a single dielectric material. s

It can thus be seen that the present invention provides an improved device that will provide rapid scanning of a radar beam. Also that the device of the present invention provides means for scanning in sawtooth fashion with very fast switching action.

Obviously many modificatons and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A scanning antenna device comprising,

a stationarily mounted reflector,

a waveguide radiator having an aperture for emitting radiant energy, said radiator being concentrically mounted relative to said reflector with said aperture extending beyond said reflector,

a cylindrical splash plate rotatably mounted to said reflector adjacent said aperture of said radiator for reflecting energy from said radiator to said reflector,

means for rotating said cylindrical splash plate about its longitudinal axis, and

means on said cylindrical splash plate for effecting a scan pattern to said reflected energy.

2. A scanning antenna device as. set forth in claim 1 wherein said means on said cylindrical splash plate for effecting a scan pattern to said reflected energy comprises at least one off-center trough spiraling around the periphrey of said cylindrical splash plate.

3. A scanning antenna device as set forth in claim 1 wherein said means on said cylindrical splash plate for effecting a scan pattern to said reflected energy comprises bands of dielectric material spiraling around the periphery of said cylindrical splash plate.

4. A scanning antenna device as set forth in claim 1 wherein said means on said cylindrical splash plate for effecting a scan pattern to said reflected energy comprises first and second off-centered troughs spiraling around the periphery of said cylindrical splash plate whereby said scan pattern is of a sawtooth configuration.

No references cited.

ELI LIEBERMAN, Acting Primary Examiner. 

1. A SCANNING ANTENNA DEVICE COMPRISING, A STATIONARILY MOUNTED REFLECTOR, A WAVEGUIDE RADIATOR, HAVING AN APERTURE FOR EMITTING RADIANT ENERGY, SAID RADIATOR BEING CONCENTRICALLY MOUNTED RELATIVE TO SAID REFLECTOR WITH SAID APERTURE EXTENDING BEYOND SAID REFLECTOR, A CYLINDRICAL SPLASH PLATE ROTATABLY MOUNTED TO SAID REFLECTOR ADJACENT SAID APERTURE OF SAID RADIATOR FOR REFLECTING ENERGY FROM SAID RADIATOR TO SAID REFLECTOR, MEANS FOR ROTATING SIAD CYLINDRICAL SPLASH PLATE ABOUT ITS LONGITUDINAL AXIS, AND 